Isolation of a polyethylene-degrading strain from farm soil

Abstract:

[Objective] The main component of agricultural mulch film is polyethylene. Because it is difficult to be degraded, its waste often causes "white pollution". In this study, polyethylene degrading bacteria were screened from the soil covered with agricultural mulch all the year round, and the degradation efficiency of polyethylene products was also explored. [Methods] Polyethylene-degrading bacteria were enriched, screened and purified using the inorganic salt medium with polyethylene as the sole carbon source. The isolated bacteria were identified by colony, morphological staining, physiological and biochemical characteristics and 16S rRNA gene phylogenetic analysis. The growth curves of isolated strain were detected under different concentrations (0, 0.05%, 0.10% 0.25%, 0.50%, 1%, 2% and 3%) of polyethylene. Finally, the biodegradation of the agricultural mulch film was detected using scanning electron microscopy and light microscopy. [Results] A strain (named as SW1) which could degrade polyethylene was isolated from soil and identified as of Nocardia sp. The growth of SW1 was dependent on the concentration of polyethylene. It grew fastest in the inorganic salt medium containing 2% polyethylene. At 48 h, the concentration of the bacterial solution began to increase; at 60 h, it reached the maximum. Meanwhile, no growth was found in the inorganic salt medium without polyethylene. In the inorganic salt medium containing agricultural mulch film, after culture at 35℃ for 15 d, a large number of bacteria were observed to be embedded in the film or attached to the surface of the film by scanning electron microscopy, the surface of the film was rough, and began to be damaged. After culture for 60 d, the membrane of the inoculated group was damaged in a large area and cavity appeared. [Conclusion] Nocardia sp. SW1 isolated from farm soil can degrade polyethylene products effectively. This study enriches the degradation microbial resources of polyethylene products, and provides scientific data and reference for the biodegradation of polyethylene plastic waste.

Key words:polyethylene;plastics;farm film;actinomycete;Nocardia;degradation